Beam interpolating system

ABSTRACT

CLAIM 1. In a sonar receiving system including means for effectively forming a plurality of receiving beams, each beam representable by a composite signal comprising signals received from another azimuth range the effective centerline of each beam having an azimuth in the center of said azimuth range, said sonar receiving system further including processing and computing means for processing each composite signal to detect the range of a target having an azimuth within the azimuth range of one of said beams, an improved system for interpolating the composite signal in which a target has been detected to resolve the azimuth of the target with respect to the azimuth of the centerline of said beam comprising: means for splitting a composite signal representative of a receiving beam in which a target has been detected into a pair of signals representative of a pair of beams which are parallel to said centerline and equidistantly disposed with respect thereto; a pair of multibit delay lines, coupled to receive said pair of signals; A PLURALITY OF ANALOG STORING UNITS, EACH UNIT, CORRESPONDING TO A DIFFERENT AZIMUTH DEVIATION WITH RESPECT TO THE AZIMUTH OF SAID CENTERLINE, BEING COUPLED TO TWO BITS OF SAID PAIR OF DELAY LINES; MEANS FOR INTEGRATING IN EACH OF SAID STORING UNITS ANALOG SIGNALS AS A FUNCTION OF THE PHASE CORRELATION OF SIGNALS IN TWO DIFFERENT BITS OF SAID PAIR OF DELAY MEANS, THE TWO BITS HAVING SIGNALS EXHIBITING A MAXIMUM PHASE CORRELATION BEING RELATED TO THE AZIMUTH DEVIATION OF SAID TARGET FROM THE AZIMUTH OF SAID CENTERLINE; MEANS FOR SCANNING SAID PLURALITY OF STORING UNITS TO DETECT THE UNIT COUPLED TO THE TWO BITS HAVING SIGNALS WHICH EXHIBIT A MAXIMUM OF PHASE CORRELATION; AND MEANS FOR PROVIDING AS A FUNCTION OF THE DETECTED UNIT AN OUTPUT SIGNAL WHICH INDICATES THE AZIMUTH DEVIATION OF THE TARGET FROM THE AZIMUTH OF SAID CENTERLINE.

United States atent [72] Inventor Fausto V Taddeo Anaheim, Calif. [21]Appl. No. 477,682 [22] Filed Aug. 6, 1965 [45] Patented May 18, 1971[73] Assignee Hughes Aircraft Company Culver City, Calif.

[54] BEAM INTERPOLATING SYSTEM 14 Claims, 6 Drawing Figs. [52] [1.8. CI340/3, 340/6. 340/16, 343/113 [51] Int. Cl G0ls 9/66 [50] Field ofSearch 340/3, 6,

16;343/100.6, 100.7, 5 (DP), 113 [56] References Cited UNITED STATESPATENTS 2,865,015 l2/l958 Butz, Jr. 340/3X 2,897,351 7/1959 Melton(340/6) 3,144,631 8/1964 Lustig et al 340/3 3,163,844 12/1964 Martin340/6 Primary Examiner-Rodney D. Bennett, Jr. Assistant -ExaminerMalcolmF. l-lubler Att0rneys-.lames K. Haskell and Walter J Adam CLAIM:CLAIM 1. In a sonar receiving system including means for effectivelyforming a plurality of receiving beams,

each beam representable by a composite signal comprising signalsreceived from another azimuth range the effective centerline of eachbeam having an azimuth in the center of said azimuth range, said sonarreceiving system further including processing and computing means forprocessing each composite signal to detect the range of a target havingan azimuth within the azimuth range of one of said beams, an improvedsystem for interpolating the composite signal in which a target has beendetected to resolve the azimuth of the target with respect to theazimuth of the centerline of said beam comprising: means for splitting acomposite signal representative of a receiving beam in which a targethas been detected into a pair of signals representative of a pair ofbeams which are parallel to said centerline and equidistantly disposedwith respect thereto; a pair of multibit delay lines, coupled to receivesaid pair of signals;

a plurality of analog storing units, each unit, corresponding to adifferent azimuth deviation with respect to the azimuth of saidcenterline, being coupled to two bits of said pair of delay lines; meansfor integrating in each of said storing units analog signals as afunction of the phase correlation of signals in two different bits ofsaid pair of delay means, the two bits having signals exhibiting amaximum phase correlation being related to the azimuth deviation of saidtarget from the azimuth of said centerline; means for scanning saidplurality of storing units to detect the unit coupled to the two bitshaving signals which exhibit a maximum of phase correlation; and meansfor providing as a function of the detected unit an output signal whichindicates the azimuth deviation of the target from the azimuth of saidcenterline.

PATENTED MAY 1 819?! SHEET 3 OF 5 PAT ENTED MAY 1 8 um SHEET k UF 5 BEAMINTERPQLATING SYSTEM used in the early radaror sonar systems was toderive direction or beam infomration by noting the relative orientationof a single antenna lobe or beam which results in a maximum signal.Since then some methods have been developed to improve the direction orbearing resolution of a target over that which can be obtained fromnoting the maximum signal from a single lobe or beam.

These methods, in general, are based on the derivation of an errorsignal or difference signal as a function of the response from two beampatterns critically oriented with respect to each other. Through thedirection resolution is improved, the circuitry necessary to employ anyof the methods is very complex, generally requiring multiamplificationchannels and phase detection circuits which must be carefully adjustedand balanced in order for the error signal to be of any valuablesignificance.

In one method, hereafter referred to as the amplitude method, an errorsignal is produced as the amplitude difference of two signals. Anantenna system is used which is capable of producing two receivingpatterns offset by a critical amount from a truev receiving direction ofa beam. The true receiving direction is accurately resolvedby noting thecenter angle of the beams where the two signals therefrom are equal.This method is quite sensitive to any gain instability of the twoamplification stages, used to amplify the signals of the two beams.Also, since measurements are not made at the maximum points on the twobeams, the method can only be employed whenthe signal-to-noise ratio isvery high.

In another method, a comparison is made of the response of two signalreceivers or transducers to signals from a source at different distancesfrom their effective centers, and noting the phase difference betweenthe received signals resulting from the difierent travel time of thesignals to the two receivers. The latter-described system lessens thesignal-to-noise ratio limitation and the high gain stabilityrequirements of the amplitude method. However, such a method requireseither the services of a highly trained operator who interpolates thesignals on the basis of the instantaneous phase angle therebetween,which are displayed on a display console, or complex correlationcircuitry which performs the correlation of two signals for successivelydifierent arrival angles or directions. However, in order to perform thecorrelation process on signals from many different directionssimultaneously, a considerable amount of storage capacity and relatedphase detection equipment is required. For example, witha pulse width ofone section, and a carrier frequency of 8 kilocycles, nearly 3 million(360X8XlO bits of storage are required to realize a theoreticaldirection resolution of 1. Thus, a need exists for a system which iscapable of resolving target direction with great accuracy, but which isnot limited by.

limitations characteristic of the prior art systems and methods.

Accordingly, it is an object to provide a novel signal interpolatingsystem which is capable of providing accurate target directionresolution.

Another object is the provision of a system for accurately resolving thedirection of a target, the system being less complex and sensitive thancomparable prior art systems.

Yet another object of the invention is to provide a system forinterpolating signals received in a target detection system to deriveaccurate target direction. The novel system incorporates a minimum ofstorage circuitry and is considerably less sensitive to small signalgain variations than prior art systems.

Still a further object is to provide a novel beam interpolating systemfor accurately resolving the direction of each of a plube within aparticular azimuth range by subdividing the range, V

into a selected number of azimuth subdivisions and detennining which ofthe subdivisions exhibits a maximum correlation when two signals relatedto the particular subdivision are cross correlated. Briefly, the target.detection system includes an array comprising a plurality of receiversor staves. Basically, a stave may be defined as an arrangement of one ormore sound wave transducers arranged in a line, generally perpendicularto the detection of the received sound wave or signal. The outputs ofdifferent stave combinations are combined to form a plurality ofcomposite signals. Each composite signal is a function of the signalsreceived from a different azimuth range, affected by any unidentifiedtargets detected therein. In the following description, the'compositesignals will also be referred to as beams or as signals representingbeams directed to different azimuth ranges, used to detect unidentifiedtargets therein.

The composite signals or beams are supplied to a beam processor whichincludes a display console and a computer. An operator, viewing eachcomposite signal or beam displayed on a display surface of the console,"detennines whether a target is detected in anyof the displayed beams.vWhen a target is detected, the operator, by means of control switches onthe display console, energizes the computer to provide a beam number,indicating in which beam the target was detected. The computer alsoprovides a target range number, indicating the range limits within whichthe target is assumed to be and an azimuth resolution number to beexplained hereafter. The beam number is decoded and used to select theappropriate set of staves, the outputs of which form the compositesignal or beam which looks at the target.

The outputs of the particular set of staves is supplied to the novelsystem of the invention which separates the composite signal into twosignals which may be thought of as representing two parallel beams.Thereafter, the signal representing each beam is clipped and clockedinto a multibit shift register, which is used as a signal delay device.The number of bits of both registers equals the number of the azimuthsubdivisions into which each azimuth range is divided. Signals,returning from a target and combined so as to be represented by the twobeams, are cross correlated by performing a bit-by-bit comcenter of thetwo parallel beams. Thus, the actual azimuth of the target is resolvedwith respect to the center of the two beams within one azimuthsubdivision value. By varying the clocking rate of the two shiftregisters, the effective phase shift and therefore azimuth deviationrepresented by each bit may be varied to control the degree to which theactual target azimuth may be resolved. 1

The novel features that are considered characteristic of this inventionare set forth with particularity in the appended claims. The inventionitself both as to its organization and method of operation, as well asadditional objects and advantages thereof, will best be understood fromthe following description when read in connection with the accompanyingdrawings, in which:

FIG. 1 is a block diagram of the novel beam interpolating system of-thepresent invention;

FIG. 2 is a diagram useful in explaining the formation of a plurality ofbeams from signals received by an array of receivers;

FIG. 3 is a diagram useful in explaining the split beam techniqueemployed in the present invention;

FIGS. 4a and 4b are a combination schematic and block diagram of theembodiment shown in FIG. 1; and

FIG. 5 is a partial diagram of another embodiment of the invention.

The novel teachings of the invention will hereafter be explained inconjunction with a sonar system for detecting unidentified targetsunderwater. It should be appreciated however that the specificembodiment and various values referred to hereafter should not beregarded as a limitation of the invention but rather as one examplethereof.

Attention is now directed to FIG. I which is a simplified block diagramof the beam interpolator, also referred to as a beam interpolatingsystem, of the present invention. The system used in conjunction with asonar display and computer stage II, hereafter also referred to as thestage II, in a sonar receiving system. It is assumed that in the sonarreceiving system which is used to provide range and azimuth data foreach target detected underwater, a plurality of signal receivers orstaves designated S,-S are arranged to simultaneously receive signalsafter being amplified in amplifiers A -A are supplied to the stage II.The stage is assumed to include beam forming circuitry, which combinethe energy from selected sets of staves, to form a plurality ofcomposite signals, which may be thought of as representing beams,oriented in all directions. Each composite signal or beam is processedto determine whether a target is located in the azimuth rangecorresponding to the beams orientation.

In a sonar receiving system utilizing 48 staves, 48 composite signals orbeams are formed, each beam having an azimuth range of 75. Techniques ofbeam forming, whether by analog or digital means, are well known in theart and therefore will not be further explained. For explanatorypurposes, it is assumed that each composite signal or beam is formed bycombining the signals of a set of i6 staves. Conventionally, eachcomposite signal or beam is processed in a receiving system, such asstage 11,-to determine whether a target is located in the azimuth rangeof the beam. The receiving system also includes circuitry arrangementsknown in the art to provide range data of a detected target.

Referring to FIG. 2, therein is shown a receiver array 20 having stavesS,--S distributed about a center 20c. A composite signal which may berepresentative of a beam 25 is formed by combining the signals receivedby staves 8 -5 and S,S,, while staves 5 -8 and S,S are used to form beam26. Beam 27 is formed by combining the outputs of staves 8 -5 and S,S01, 02 and 03 represent the azimuth ranges of beams 25, 26 and 27, eachrange being equal to 75. It is appreciated by those familiar with theart that known processing techniques may be used to analyze beam 25 inorder to determined if a target is in the azimuth range 01, in whichcase the range of the target is derived. However in order to obtaintarget azimuth to a higher accuracy than that represented by the azimuthrange of 75, some technique must be employed to further analyze orinterpolate the beam 25 in order to narrow down, or more preciselyderive, the target azimuth.

According to the teachings of the present invention, this may beaccomplished by producing a beam number in the stage 11 which representsthe beam in which a target has been detected. Assuming that in beam 25,which is reproduced in FIG. 3 to which reference is made herein, atarget T has been detected. The stage 11 will supply a beam number,related to beam 25, to a beam selection switch 32 (FIG. 1) which forms apart of the novel beam interpolating system of the present invention.The function of switch 32 is to select the appropriate set of l6 staveamplifier outputs representing the beam which looks at the particulartarget. In the present example, beam 25 looks at target T, so that theoutputs of A --A and A,'A are selected by switch 32 and supplied to anamplification stage 34, wherein the output of each A amplifier isfurther amplified and supplied to a split beam former 36.

Effectively, in the split beam former, the outputs of the 16 staves usedto form the composite signals represented by beam 25, are split into twogroups to form two signals. One signal is formed from the outputs ofstaves 8 -8 and S and the other signal is formed from the outputs ofstaves 8; through S The two signals may be thought of as comprising orbeing 7 representative of two parallel beams designated in FIG. 3 as 25Rand 25L. Since each of the parallel beams is a function of the outputsof only half the number of staves used to form the composite signalrepresentative of beam 25, each of the parallel beams is twice as wideas beam 25, i.e. 15. The term split beam former is used to identify acircuit which divides the outputs from the 16 staves to provide twosignals representative of two parallel beams. The signals represented bybeams 25R and 25L are clipped by clipper amplifiers 38R and 38Lrespectively, the outputs of which are respectively clocked into 2multibit shift registers 40R and 40L. The clock pulses are supplied froma clock generator which provides pulses at rates controlled by stage 11.

As seen from FIG. I, each of the shift registers is shown comprising 15bits. The shift registers are used as signal delay devices. Signalsreturning from a target which is exactly at the center of the two beams25R and 25L designated by line 45 arrives at the inputs of the two shiftregisters in phase. However, as the target moves to one side, such astarget T shown to the left of line 45, or the other side of the centerof the two beams, the signal transit time from the target to each beamdiffers slightly. This difference in transit time is detected byperforming a bit-by-bit comparison of the contents of the two shiftregisters in a correlation unit 50 and accumulating the results of eachcomparison in a separate analog storing stage therein.

As previously pointed out, the sonar display and computer stage 11, whenanalyzing beam 25, detects the target T deriving range data thereof. Therange of target T is designated by line R The stage in response to therange of target T generates a range gate AR At the start of the gate ARthe stage 11, through a range gate generator 52, enables the correlationunit 50 to perform the required correlation and accumulation processwhich ends at the end of the range gate. Thereafter, the unit 50 isscanned, as will be explained hereafter in greater detail, to search outthe analog storing stage which has a maximum value or level. Such unitrepresents the azimuth deviation between the center of the two parallelbeams (line 45 in FIG. 3) and the actual location of the target. Theazimuth deviation of target T is represented in FIG. 3 by A0 The azimuthdeviation A0 is then transmitted to stage II in order to adjust thepreviously determined azimuth of target T which was based entirely onthe azimuth range (7.5") of beam 25.

For a more complete description of the invention, reference is made toFIGS. 4a and 4b which together comprise a combination schematic andblock diagram of the novel beam interpolating system. As previouslyexplained, the sonar display and computer stage 11, after detecting atarget in any of the beams, such as beam 25, supplies a beam number toactuate beam selection switch 32. The stage 11 also supplies range gatesignals to range gate generator 52, in order to control the correlationunit 50 to perform the comparisons of signals received during a rangegate AR from a target at a range R. In FIG. 4a, a multibit register 60,which is assumed to be part of the output of stage 11, is shownconnected to the various circuits of the system. Six bits (1-6) of theregister are used to control the beam selection switch 32 so that theoutputs of an appropriate set of 16 staves are used to form the twosignals represented by the two parallel beams. For beam 25, the outputsof staves 8 -8 and S,--S after amplification in the related A amplifiers(FIG. 1), are supplied to amplifiers G ,G 8 and G,G of the amplificationstage 34. The G amplifiers, each of which has a very high outputimpedance, are designed to minimize phase shift over the frequency rangeof interest, since any variation in phase shift among these amplifiersdirectly contributes to error in the desired azimuth resolution.

The outputs of the 16 G amplifiers'are supplied to the split beam former36 which, in FIG. 4a, is shown comprising a multitap analog delay line,each tap being connected to theoutput of another of the G amplifiers.The two portions of the delay line 36 must be matched so that any phaseshift which occurs in one portion will also occur in the other. Thetechnique of splitting a beam into two parallel beams, by employing ananalog delay line, is presented as one example for forming the parallelbeams 25R and 25L (see FIG. 3). It should be appreciated that some otherbeam splitting technique may similarly be employed.

The locations for the outputs of the G amplifiers on the delay line 36are selected for zero phase error at the nominal value of soundpropagation velocity. Since this propagation velocity undergoes slightchanges due to environmental variations as well as apparent changes dueto own ships motion, some beam forming distortion will necessarilyoccur. These errors will exhibit themselves by slightly altering theshape of the preformed receiving beams. However, since only phasecomparison is made between the two signals received in the two beams,interpolator accuracy is not affected.

The two signals at the outputs of the two portions of delay line 36 aresupplied to clipper amplifiers 38L and 38R which clip the signals at theoutput of the split beam former 36. The clipped signals are clocked intothe registers 40L and 40R and progress down each register at a uniformrate. The rate of progress is a function of the rate of the outputspulses of generator 42, which is in turn controlled by the stage 11through the 7th bit of register 60. In the present embodiment of theinvention, it is assumed that the rate of clock pulses from generator 42is fixed at f pps.

As seen from FIG. 1, shift registers 40L and 40R are connected to thecorrelation unit 50. In FIG. 4b, unit 50 is shown comprising 30correlation gates designated L,L, and R,- R, The th bit of register 40Rand one of the bits of register 401. are connected to another of gatesL,L, Similarly, the inputs of another of gates R,R, are connected to the15th bit of 40L and one of the bits of register 40R. A third input ofeach gate is connected to a flip-flop (FF) 52a of the range gategenerator 52. Each of the gates may be thought of as a correlation gatein that an enabling or On" output is supplied therefrom when the samesignals are present in the inputs thereof connected to the registers 40Land 40R. However, for simplicity, the gates are diagrammed as AND gates.

Each of the correlation gates is associated with an analog switch and ananalog storing unit, which is diagrammed as a capacitor connectedbetween ground potential and its respective analog switch. Thus gatesL,L are associated or coupled to switches LS,--I.S respectively, whichare in turn connected to storing units LC,LC, Similarly gates R,R arecoupled to switches RS -RS which are connected to storing units RC,RC,Each of the switches is connected to a current source 65. The functionof each gate and switch associated with another storing unit is tocontrol the supply of charging current to the capacitor. Chargingcurrent is supplied from source 65 to a capacitor to increase thevoltage thereacross only when its respective analog switch is enabled.This happens only when the respective correlation gate is enabled or on"as a result of the same signals being present on both of its inputswhich are connected to the two shift registers.

If the target is exactly in the center of the two parallel beams (line45 in FIG. 3), the signals within the shift registers will be in phase.Thus, corresponding pairs of bits such as, for example, bits 15 inregisters 40L and 40R will always be in the same state. Consequently,gates L and R will be enabled to in turn enable switches LS and RSrespectively. As a result, the charge or voltage cross LC and RC willincrease. It is appreciated that only one of gates L, or R and thecircuitry associated therewith is necessary. However, the twoarrangements are shown to simplify the description of the invention.

From the foregoing, it is thus seen that each analog storing unit orcapacitor serves as an accumulator of all the comparisons made betweenthe two shift register bits associated therewith. The capacitor chargesup to a final value, which is proportional to the degree of phasecorrelation of the signals in the 2 bits. A target which slightlydeviates from the center axis of the two parallel beams will not causethe maximum correlation accumulation product to be stored forcorresponding pairs of bits since the signal'in corresponding pairs willbe out of phase. The maximum correlation product, however, will alwaysoccur for a unique pair of bits in the upper and lower registers.

As previously indicated, the function of the beam interpolating systemof the invention is to resolve, by beam interpolation, the azimuth oftarget such as T (FIG. 3) detected by stage 11 in a particular beam,such as beam 25. When detecting the target, the target range R isderived by stage 11. This range is then used to control theinterpolating system to produce signal comparisons only during theinterval of range gate AR. Namely, the comparisons are limited to aperiod during which signals are expected from a range of toarange Inorder to control the start and end of the comparison operation, to belimited to the period of the particular range gate, the system includestwo digital comparators 52b and 520 which form part of the range gategenerator 52. Nine bits (8 through 16) of register 60 are used to supplycomparator 52b with the lower range limit AR R 7 of the range gate, andanother 9 bits (17 through 25) are used to supply comparator 52c withthe upper range limit AR R 7 of the range gate. Also the two comparatorsare provided with the output of a range counter which is part of stage11 (FIG. 1).

When the two inputs to comparator 52b are equal, i.e. the lower limit ofthe range gate is reached, comparator 52b sets FF 52a to enable all thecorrelation gates Is -L and R -R so that the results of the comparisonof the signals of each pair of bits is accumulated. At the end of therange gate, i.e. at a time corresponding to comparator 52c resets FF 52ato disable the gates, thereby completing the accumulation of thecomparisons. The latter may also be thought of as the end of thecorrelation integratron process.

The output signal of comparator 520 which resets FF 52a is also suppliedto a counter (S-bit) which drives a scan switch connected across each ofthe analog storing units LC,LC and RC RC, The switch 75 sequentiallydirects the voltage, which is an analog signal or sample across each ofthe storingunits to an analog comparator 80. Comparator compares themagnitude of the voltage from each storing unit with the magnitude ofthe voltage from the preceding unit. If the magnitude of the voltage issmaller than the voltage from a preceding unit, no further actionoccurs. However, if the magnitude of the voltage is greater than thatfrom the preceding unit, then the analog comparator stores the greatervoltage magnitude. At the same time, it also enables a gate 82, so thatthe contents or number of the counter 70 is shifted into an outputregister 85. In this way the output register always contains the counternumber corresponding to the analog storing unit in which the largestvoltage or analog signal is stored. This number will be present in theoutput register when counter 70 completes its cycle, at which time itsupplies a cycle complete signal to set a flip-flop 88. When the latterflip-flop is set, it supplies a data ready signal to the stage 11- (FIG.1), indicating that the storing units have been scanned and that thenumber corresponding to the unit with the largest voltage signal is inregister 85.

When the stage 11 is ready to accept such data. an inter rogate signalfrom stage 11 sets a flip-flop 92 which activates a digital line driver95 to transfer the content of output register 85 to the stage II. Thiscontent represents the azimuth deviation of the detected target from thecenter line of the two parallel beams. The resolution of the azimuthdeviation is a function of the rate f of the clock pulses, since eachclock pulse represents a l-bit phase shift.

When FF 92 is set, it resets FF 88 and sets a system status FF 96 whichsupplies an interrogate complete signal to stage 11, indicating that thesystem is ready to interpolate the azimuth of another target. Dependingon the operation of the stage 11, when it is in condition to interpolateanother beam, it supplies a system enable signal which resets FF 96, aswell as the analog comparator by discharging the highest voltage readingstored therein from the previous interpolation operation. The systemenable signal also resets FF 92.

From the foregoing, it should be appreciated by those familiar with theart that by dividing the composite signal represented by a receivingbeam (such as beam 25) into two signals represented by two parallelbeams (such as 25L and 25R) and clocking the two signals into the twoshift registers (40L and 40R), the azimuth of a target (such as T) maybe accurately resolved, by determining the azimuth deviation of thetarget from an azimuth defined by the center line common to both beams(such as line 45). From FIG. 3, it is apparent that signals from targetT which is to the left of center line 45 will arrive at the beam 25Lprior to arriving at beam 25R. Assuming that the azimuth deviation AB is2 and that the shift registers are clockedatf so that a l-bit phaseshift corresponds to 0.5 azimuth range that it is appreciated that thesignals in the 11th bit of shift register 40L and the 15th bit ofregister 40R will be in phase. Thus, unit LC will exhibit the largestanalog signal, so that the number corresponding to it will be suppliedfrom output register 85 to the computer stage 11. It should beappreciated that as long as the clocking rate of the shift registers isfixed the azimuth range which is represented by l-bit phase shift isfixed. Thus, in the foregoing, the azimuth resolution accuracy of thesystem is limited to 0.5.

In another embodiment of the present invention the system includesadditional circuitry, which enables the system to interpolate a beam ineither of 2 incremental azimuth ranges. In either case, the systemdivides the azimuth range into 30 increments. Initially, after targetdetection the stage 11 will control the system to coarsely interpolatethe target azimuth such as within :05. Thereafter, the azimuth rangerepresented by each increment is reduced, so that the final azimuth of atarget could be resolved to a higher degree of accuracy.

For a more complete description of the invention, reference is made toFIG. 5 which is a partial block diagram of circuitry required to resolvetarget azimuth within either of two levels of accuracy. As previouslyexplained, the stage 11 controls the clock generator 42 through bit 7 ofregister 60. The generator is shown comprising a pair of oscillators 42aand 42b connected to a clock regenerator 420 through gates 42a and 42erespectively. The output of clock regenerator 420 is used to clock theshift registers 40L and 40R. The oscillators 42a and 42b generatesignals at rates f and nf respectively so that the rate at which theshift registers are clocked depends on which one of the gates 42d and42e is enabled. These gates are controlled by the signal from the stage11. Thus, a 1st bit such as a one may be used to enable gate 42d so thatthe clocking rate is f while a 2nd bit or a zero enables gate 42e toincrease the clocking rate to nf In addition to controlling the clockingrate of the shift registers, in the present embodiment of the invention,the system includes a beam offsetting delay line 36x which is interposedbetween end terminals X and X of the split beam former 36 and theclipping amplifiers 38L and 38R. Switches l q-P, connect four tap pointsof one portion of the line 36x to amplifier 38L and switches I" ,Pconnect four other tap points of the other half of the line 36x. Theswitches are controlled by an azimuth offset logic circuit 100, which isin turn energized with signals supplied from the stage 11 through bits26, 27 and 28 of register 60. The time delay between tap points forthese switches is selected so that the signals of the two parallel beams(25L and 25R) can be offset from beam center (line 45) by i4.5 in 15steps.

The complete system can now be described in connection with thefollowing example. Let us assume that in beam 25, target T is detectedby stage 11 to be at a range R To resolve its azimuth, the beaminterpolating system is enabled. A beam number 25 is supplied to beamselection switch 32 which supplies the outputs of an appropriate set ofstaves (S -S S S to form beam 25L and 25R in beam former 36. At theinstance of the lower range limit AR T FF 52a [FIG 4a] is set enablingthe correlation gates, which initiate the correlation integrationprocess. At the same time, clock generator 42 clocks the shift registersat the lower f frequency. Assuming that the rate is such that each bitphase shift is related to 0.5 azimuth, and that AO (FIG. 3) is 2, thenLC will exhibit the highest voltage. At the end of the range gate (lawFF 52a will be reset terminating the correlating integration process andinitiating the scanning of the various storing units (LC and RC) to findthe one with the highest voltage which in the present example is LC Thenumber related thereto will then be supplied from register throughdriver to the stage 11, indicating that the azimuth AO of target T is 2to the left of center line 45, within an accuracy of 0.5 which is theazimuth range of l azimuth subdivision.

To obtain a higher resolution accuracy such as, for example 0. 1, thesystem is again enabled. The generator 42 is enabled to clock the shiftregisters at a frequency nf where n is 5 since the accuracy has beenincreased from 0.5 to 0.1. Also a pair of switches from switches P,P,,,such as P and P are selected to insert fixed delays in the signals fromthe beam former 36 to the clipper amplifiers 38L and 38R in order tooffset the signals by 15 to the left of the center line 45. Thus,effectively switches P P and the azimuth offsetting delay line 36xoffset the signals of the two beams to be centered about line 4S Theoffset signals are clocked into the registers 40L and 40R at a rate nf,so that the azimuth deviation of the target T about line 4S may bedetermined to be within 0. 1.

As previously described in detail, the azimuth of the target is resolvedby performing a correlation integration during a time period duringwhich signals from the range of the target are expected to be received.This is accomplished by enabling the analog correlation unit 50 at AR Tand disabling it at AR RT-I Thus, it should be apparent that theinterpolating system may be used to resolve the azimuth of any number oftargets during a single sonar scan, provided the targets do not overlapin range. Furthermore, the azimuth of each target can be resolved withineither degree of accuracy (0.5 or 0.l) by controlling the signalsupplied from stage 11 to the clock generator 42.

From the foregoing, it should be appreciated that the use in the presentinvention of 2 multibit shift registers, in the novel arrangementhereinbefore described, greatly reduces the storage capacity, necessaryto interpolate a beam in order to resolve the azimuth of a detectedtarget. Two l-bit shift registers are used to subdivide an azimuth rangeinto 30 subdivisions or increments. Furthermore. the azimuth range suchas 05 or 0. 1 corresponding to each increment is controllable. It is afunction of the rate at which signals are clocked into the registers.

There has accordingly been shown and described herein a novel beaminterpolating system for resolving the azimuth of a target, detected tobe within an azimuth range which is related to a received beam. Itshould be appreciated that those familiar with the art may makemodifications in the specific arrangements herebefore described withoutdeparting from the true spirit of the invention. Therefore, all suchmodifications and equivalents are deemed to fall within the scope of theinvention as claimed in the appended claims.

l claim:

1. In a sonar receiving system including means for effectively forming aplurality of receiving beams, each beam representable by a compositesignal comprising signals received from another azimuth range theeffective center line of each beam having an azimuth in the center ofsaid azimuth range, said sonar receiving system further includingprocessing and computing means for processing each composite signal todetect the range of a target having an azimuth within the azimuth rangeof l of said beams, an improved system for interpolating the compositesignal in which a target has been detected to resolve the azimuth of thetarget with respect to the azimuth of the center line of said beamcomprismg:

means for splitting a composite signal representative of a receivingbeam in which a target has been detected into a pair of signalsrepresentative of a pair of beams which are parallel to said center lineand equidistantly disposed with respect thereto;

a pair of multibit delay lines, coupled to receive said pair of signals;

a plurality of analog storing units, each unit, corresponding to adifferent azimuth deviation with respect to the azimuth of said centerline, being coupled to 2 bits of said pair of delay lines;

means for integrating in each of said storing units analog signals as afunction of the phase correlation of signals in two different bits ofsaid pair of delay means, the 2 bits having signals exhibiting a maximumphase correlation being related to the azimuth deviation of said targetfrom the azimuth of said center line;

means for scanning said plurality of storing units to detect the unitcoupled to the 2 bits having signals which exhibit a maximum of phasecorrelation; and

means for providing as a function of the detected unit an output signalwhich indicates the azimuth deviation of the target from the azimuth ofsaid center line.

2. In a sonar receiving system wherein a target is detected in areceiving beam comprising signals received from a particular azimuthrange, an improved beam interpolating system for resolving the azimuthof said target by providing an output signal indicative of the deviationof the azimuth of said target from the azimuth of a center line of saidbeam comprising:

means for forming signals representative of said receiving beam splitinto two beams parallel to said center line and equidistantly disposedwith respect thereto;

two multibit delay lines each line coupled to receive signals of anotherof said two parallel beams; and

correlation means coupled to the two delay lines for correlating thephase of the signals of said two beams on a bit-by-bit comparison toprovide an output signal which indicates the deviation of the azimuth ofsaid target from the azimuth of the center line of said beam.

3. The system of claim 2 wherein said correlation means include:

a plurality of storing units;

means for coupling 2 bits each of another of said delay lines to eachstoring unit;

first means for controlling the storing of signals in each storing unitas a function of the phase correlation of the signals in the 2 bitscoupled to said storing unit, the relationship of the phases of saidsignals being related to the deviation of the azimuth of said targetwith respect to the azimuth of said center line; and

second means for sequentially scanning said storing units to providesaid output signal as a function of the storing unit having a maximum ofsignals stored therein.

4. The system of claim 3 wherein each of said 2 multibit delay linescomprises a multibit shift register said system including clock pulsegenerating means for providing clock pulses at a selected rate; and

means for energizing the two shift registers with said clock pulses toclock the signals of said two parallel beams into said registers at saidselected rate, the time required for signals to advance I bit in one ofsaid registers representing a predetermined azimuth deviation from theazimuth of said center line.

5. The system of claim 4 further including:

range gate generating means responsive to range gating signals from saidsonar receiving system for controlling said analog correlation means tostore signals in said storing units only during a predetermined periodrelated to the range of said target from said sonar receiving system.

6. The system of claim 5 wherein said range gate generating meansinclude means for enabling said correlation means to store signals insaid storing means when said receiving system receives signals from arange Ira- R being the detected range of said target and AR being aselected incremental range portion, said range gate generating meansinclude means for disabling said correlation means when said sonarreceiving system receives signals from a range 7. In combination with asonar receiving system wherein received signals are combined to form aplurality of composite signals representative of a plurality of beams,each beam being representable by signals received from another azimuthrange, the system including processing and computing means to processeach beam and detect a target having an azimuth within the azimuth rangeof the particular beam, said system further providing a signalindicative of the range of the detected target, a signal interpolatingsystem for resolving the azimuth of the detected target within saidazimuth range with respect to the azimuth of a center line of said beamcomprismg:

first means responsive to the signals received from another azimuthrange for forming a pair of signals representative of a pair of beamsparallelly aligned with the center line of the beam representable by thesignals received from said azimuth range and equidistantly disposed withrespect thereto;

a pair of multibit shift registers each coupled to said first means toreceive another of said pair of signals;

means for clocking said pair of signals into said pair of shiftregisters at a predetermined rate, the time required for a signal toadvance in one of said registers by 1 bit corresponding to a phase shiftbetween related signals of said pair of beams received from a targetwhich has an azimuth deviating by a selected azimuth increment from theazimuth of said center line;

correlation means coupled to each of the bits of said pair of shiftregisters for correlating the phase of the signals in different pairs ofbits and detecting the pair of bits having signals with a maximum phasecorrelation; and

lll

output means responsive to the pair of bits having signals with themaximum phase correlation for providing an output signal whichrepresents the azimuth deviation of the azimuth of said target from theazimuth of said center line. the accuracy of said selected azimuthincrement which is a function of the rate signals are clocked in saidshift registers.

8. The combination of claim 7 wherein said correlation means include aplurality of analog storing units, each unit being coupled to anotherpair of bits of said pair of shift registers for accumulating analogsignals as a function of the phase correlation of the signals in saidpair of bits, the magnitude of the analog signals accumulated during apredetermined period in each of said units being related to thecorrelation product of the pair of bits coupled thereto in said pair ofshift registers and the actual azimuth deviation of the azimuth of saidtarget with respect to the azimuth of said center line, and said outputmeans including means for scanning said plurality of storing units anddetecting the unit storing analog signals having a maximum magnitude toprovide said output signal which represents the azimuth deviation of theazimuth of said target from the azimuth of said center line.

9. The combination of claim 8 wherein said signal interpolating systemfurther includes range gate means for controlling the accumulation ofsaid analog signals to a predetermined period which is related to aperiod during which said sonar receiving system receives signals fromsources located between ranges where R, is the detected range of saidtarget and AR is a predetermined range interval.

10. The combination of claim 7 wherein said signal inter polating systemfurther includes means for controlling said means for clocking wherebysignals are clocked into said shift registers at one of a plurality ofselected rates to control the azimuth increment represented by the timerequired for a signal to advance in either of said shift registers by 1bit.

11. The combination of claim 10 wherein said correlation means include aplurality of analog storing units, each unit being coupled to anotherpair of bits of said pair of shift registers for accumulating analogsignals as a function of the phase correlation of the signals in saidpair of bits, the magnitude of the analog signals accumulated during apredetermined period in each of said units being related to thecorrelation product of the pair of bits coupled thereto in said pair ofshift registers and the actual azimuth deviation of the azimuth of saidtarget with respect to the azimuth of said center line, and said outputmeans including means for scanning said plu- AR R T and AR R 2 1 where Ris the detected range of said target and AR is a predeterminedrangeinterval. I

3. The combination of claim 10 said signal interpolating system furtherincluding beam offsetting means responsive to signals of the processingand computing means of said sonar receiving system for electronicallyoffsetting the center of said pair of beams from said center line andaligning said center with a target line directed to said detected targetto resolve the azimuth of said target with respect to said target line.

14. In a target detection receiving system including a plurality ofreceivers, means for forming a plurality of receiving beams, each beamcomprising signals received from another azimuth range and processingand computing means for deriving the range of a target detected in oneof said receiving beams an improvedsystem for interpolating saidreceiving beam to resolve the azimuth of said target with respect to theazimuth range of said receiving beam comprising:

means for separating the signals which comprise said beam into twosignals which effectively represent two parallel beams equally spacedwithin respect to a center line having an azimuth which is centered inthe azimuth range of one of said receiving beams; a pair of delay means;I means for supplying said two signals which effectively comprise saidtwo parallel beams to said pair of delay lines;

means coupled'tosaid delay lines for correlating signals receivedtherefrom to provide a plurality of analog signals, each analog signalbeing a function of the phase correlation between another set of twosignals from said delay lines; and

means for scanning said analog signals and detecting the analog signalsrelated to the two signals having the highest degree of phasecorrelationto determine the azimuth of said target as a function of the azimuthdeviation represented by said detected analog signal with respect to theazimuth represented by said center line.

1. In a sonar receiving system including means for effectively forming aplurality of receiving beams, each beam representable by a compositesignal comprising signals received from another azimuth range theeffective center line of each beam having an azimuth in the center ofsaid azimuth range, said sonar receiving system further includingprocessing and computing means for processing each composite signal todetect the range of a target having an azimuth within the azimuth rangeof 1 of said beams, an improved system for interpolating the compositesignal in which a target has been detected to resolve the azimuth of thetarget with respect to the azimuth of the center line of said beamcomprising: means for splitting a composite signal representative of areceiving beam in which a target has been detected into a pair ofsignals representative of a pair of beams which are parallel to saidcenter line and equidistantly disposed with respect thereto; a pair ofmultibit delay lines, coupled to receive said pair of signals; aplurality of analog storing units, each unit, corresponding to adifferent azimuth deviation with respect to the azimuth of said centerline, being coupled to 2 bits of said pair of delay lines; means forintegrating in each of said storing units analog signals as a functionof the phase correlation of signals in two different bits of said pairof delay means, the 2 bits having signals exhibiting a maximum phasecorrelation being related to the azimuth deviation of said target fromthe azimuth of said center line; means for scanning said plurality ofstoring units to detect the unit coupled to the 2 bits having signalswhich exhibit a maximum of phase correlation; and means for providing asa function of the detected unit an output signal which indicates theazimuth deviation of the target from the azimuth of said center line. 2.In a sonar receiving system wherein a target is detected in a receivingbeam comPrising signals received from a particular azimuth range, animproved beam interpolating system for resolving the azimuth of saidtarget by providing an output signal indicative of the deviation of theazimuth of said target from the azimuth of a center line of said beamcomprising: means for forming signals representative of said receivingbeam split into two beams parallel to said center line and equidistantlydisposed with respect thereto; two multibit delay lines each linecoupled to receive signals of another of said two parallel beams; andcorrelation means coupled to the two delay lines for correlating thephase of the signals of said two beams on a bit-by-bit comparison toprovide an output signal which indicates the deviation of the azimuth ofsaid target from the azimuth of the center line of said beam.
 3. Thesystem of claim 2 wherein said correlation means include: a plurality ofstoring units; means for coupling 2 bits each of another of said delaylines to each storing unit; first means for controlling the storing ofsignals in each storing unit as a function of the phase correlation ofthe signals in the 2 bits coupled to said storing unit, the relationshipof the phases of said signals being related to the deviation of theazimuth of said target with respect to the azimuth of said center line;and second means for sequentially scanning said storing units to providesaid output signal as a function of the storing unit having a maximum ofsignals stored therein.
 4. The system of claim 3 wherein each of said 2multibit delay lines comprises a multibit shift register said systemincluding clock pulse generating means for providing clock pulses at aselected rate; and means for energizing the two shift registers withsaid clock pulses to clock the signals of said two parallel beams intosaid registers at said selected rate, the time required for signals toadvance 1 bit in one of said registers representing a predeterminedazimuth deviation from the azimuth of said center line.
 5. The system ofclaim 4 further including: range gate generating means responsive torange gating signals from said sonar receiving system for controllingsaid analog correlation means to store signals in said storing unitsonly during a predetermined period related to the range of said targetfrom said sonar receiving system.
 6. The system of claim 5 wherein saidrange gate generating means include means for enabling said correlationmeans to store signals in said storing means when said receiving systemreceives signals from a range RT being the detected range of said targetand Delta R being a selected incremental range portion, said range gategenerating means include means for disabling said correlation means whensaid sonar receiving system receives signals from a range
 7. Incombination with a sonar receiving system wherein received signals arecombined to form a plurality of composite signals representative of aplurality of beams, each beam being representable by signals receivedfrom another azimuth range, the system including processing andcomputing means to process each beam and detect a target having anazimuth within the azimuth range of the particular beam, said systemfurther providing a signal indicative of the range of the detectedtarget, a signal interpolating system for resolving the azimuth of thedetected target within said azimuth range with respect to the azimuth ofa center line of said beam comprising: first means responsive to thesignals received from another azimuth range for forming a pair ofsignals representative of a pair of beams parallelly aligned with thecenter line of the beam representable by the signals received from saidazimuth range and equidistantly disposed with respect thereto; a pair ofmultibit shift registers each coupled to said first means to receiveanother of said pair of signals; Means for clocking said pair of signalsinto said pair of shift registers at a predetermined rate, the timerequired for a signal to advance in one of said registers by 1 bitcorresponding to a phase shift between related signals of said pair ofbeams received from a target which has an azimuth deviating by aselected azimuth increment from the azimuth of said center line;correlation means coupled to each of the bits of said pair of shiftregisters for correlating the phase of the signals in different pairs ofbits and detecting the pair of bits having signals with a maximum phasecorrelation; and output means responsive to the pair of bits havingsignals with the maximum phase correlation for providing an outputsignal which represents the azimuth deviation of the azimuth of saidtarget from the azimuth of said center line, the accuracy of saidselected azimuth increment which is a function of the rate signals areclocked in said shift registers.
 8. The combination of claim 7 whereinsaid correlation means include a plurality of analog storing units, eachunit being coupled to another pair of bits of said pair of shiftregisters for accumulating analog signals as a function of the phasecorrelation of the signals in said pair of bits, the magnitude of theanalog signals accumulated during a predetermined period in each of saidunits being related to the correlation product of the pair of bitscoupled thereto in said pair of shift registers and the actual azimuthdeviation of the azimuth of said target with respect to the azimuth ofsaid center line, and said output means including means for scanningsaid plurality of storing units and detecting the unit storing analogsignals having a maximum magnitude to provide said output signal whichrepresents the azimuth deviation of the azimuth of said target from theazimuth of said center line.
 9. The combination of claim 8 wherein saidsignal interpolating system further includes range gate means forcontrolling the accumulation of said analog signals to a predeterminedperiod which is related to a period during which said sonar receivingsystem receives signals from sources located between ranges and where RTis the detected range of said target and Delta R is a predeterminedrange interval.
 10. The combination of claim 7 wherein said signalinterpolating system further includes means for controlling said meansfor clocking whereby signals are clocked into said shift registers atone of a plurality of selected rates to control the azimuth incrementrepresented by the time required for a signal to advance in either ofsaid shift registers by 1 bit.
 11. The combination of claim 10 whereinsaid correlation means include a plurality of analog storing units, eachunit being coupled to another pair of bits of said pair of shiftregisters for accumulating analog signals as a function of the phasecorrelation of the signals in said pair of bits, the magnitude of theanalog signals accumulated during a predetermined period in each of saidunits being related to the correlation product of the pair of bitscoupled thereto in said pair of shift registers and the actual azimuthdeviation of the azimuth of said target with respect to the azimuth ofsaid center line, and said output means including means for scanningsaid plurality of storing units and detecting the unit storing analogsignals having a maximum magnitude to provide said output signal whichrepresents the azimuth deviation of the azimuth of said target from theazimuth of said center line.
 12. The combination of claim 11 whereinsaid signal interpolating system further includes range gate means forcontrolling the accumulation of said analog signals to a predeterminedperiod which is related to a period during which said sonar receivingsystem receives signals from sources located between ranges and where RTis the detected rangE of said target and Delta R is a predeterminedrange interval.
 13. The combination of claim 10 said signalinterpolating system further including beam offsetting means responsiveto signals of the processing and computing means of said sonar receivingsystem for electronically offsetting the center of said pair of beamsfrom said center line and aligning said center with a target linedirected to said detected target to resolve the azimuth of said targetwith respect to said target line.
 14. In a target detection receivingsystem including a plurality of receivers, means for forming a pluralityof receiving beams, each beam comprising signals received from anotherazimuth range and processing and computing means for deriving the rangeof a target detected in one of said receiving beams an improved systemfor interpolating said receiving beam to resolve the azimuth of saidtarget with respect to the azimuth range of said receiving beamcomprising: means for separating the signals which comprise said beaminto two signals which effectively represent two parallel beams equallyspaced within respect to a center line having an azimuth which iscentered in the azimuth range of one of said receiving beams; a pair ofdelay means; means for supplying said two signals which effectivelycomprise said two parallel beams to said pair of delay lines; meanscoupled to said delay lines for correlating signals received therefromto provide a plurality of analog signals, each analog signal being afunction of the phase correlation between another set of two signalsfrom said delay lines; and means for scanning said analog signals anddetecting the analog signals related to the two signals having thehighest degree of phase correlation to determine the azimuth of saidtarget as a function of the azimuth deviation represented by saiddetected analog signal with respect to the azimuth represented by saidcenter line.